Coded OFDM over short range underwater optical wireless channels using LED

This paper investigates the performance of coded orthogonal frequency division multiplexing (OFDM) in underwater optical wireless communications (UWOWC). Low density parity check (LDPC) and turbo code are used in conjunction with a 16 quadrature amplitude modulation (16-QAM) scheme. The channel impulse response (CIR) is simulated via the Monte Carlo modelling of light (MCML) approach using the Henyey-Greenstein model of scattering phase function. A clean seawater environment, and two types of realistic turbidity for coastal and harbour waters are considered. A one-tap minimum mean squared error frequency domain equalizer (MMSE-FDE) is used for equalization. Its coefficients are designed using a comb-type channel estimation (CE) arrangement and interpolation. The bit error rate (BER) performances obtained via simulation demonstrate that turbo code with the Max-Log Map decoder outperform LDPC with an SPA decoder, with improvements ranging between 2 to 4 dB at a 10
^-3
BER for three water types. It is also clear that the coded system provides a noteworthy performance improvement compared to the uncoded case, thus enhancing the reliability of UWOWC links at high data rates.